Need help on entity framework projections

Question

I have two entities: Customer and address

CUSTOMER
---------
Id
Name
Addresses

ADDRESS
---------
Id
CustomerId
Street
City
Country
IsPrimaryAddress

Customer can have multiple address but only one primary address. I need to get a list of customers along with its primary address only. How can i get it with a single call to the database?

Answer 1

Just create a new type that is not an entity and return this from your query:

using (var db = new YourDbContext())
{
    var results = 
        from customer in db.Customers
        let primaryAddress = customer.Addresses.Single(a => a.IsPrimaryAddress)
        select new CustomerQueryResult
        {
            Id = customer.Id,
            Name = customer.Name,
            Address = primaryAddress
        };

    return results.ToArray();
}